The storage of hydrogen, as a gaseous fuel for the operation of fuel cells, has been proposed by Justi, U.S. Pat. No. 3,350,229. This reference appears to recite storage, at about -183.degree. C. and atmospheric pressure, sorption of the order of 6 mmol/cm.sup.3 of porous carbon, which has an apparent density of 0.44 g/cm.sup.3. This corresponds roughly to a hydrogen adsorption capacity of 13.6 mmol/g. However, this figure is derived from an imaginary "adsorption capacity," expressed in terms of cm.sup.3 of hydrogen, reduced to 760 torr at 0.degree. C., per cm.sup.3 of adsorbent, measured at -183.degree. C., cited by Jaeckel, "Kleinste Drucke ihre Messung and Erzeugung," Springer-Verlag, Berlin (1950) at page 210. Measured values for hydrogen adsorption at 1 atmosphere at cryogenic temperatures (-197.degree. C. to -185.degree. C.) of various carbons fall in a range between about 7.3 and 8.7 mmol of hydrogen/g of the carbon.
Heyland, in U.S. Pat. No. 1,901,446, has proposed storing liquefied gases on bodies such as silica gel or charcoal, indicating that silica gel is the better adsorbent.
It has been proposed by Teitel, in U.S. Pat. No. 4,211,537, to store hydrogen in a supply means, comprising a metal hydride hydrogen storage component and a microcavity hydrogen storage component, which in tandem provide hydrogen to an apparatus requiring hydrogen.
Woollam (U.S. Pat. No. 4,077,788) recites storage of atomic hydrogen, at liquid helium temperatures, in the presence of a strong magnetic field, in exfoliated layered materials, such as molybdenum disulfide or graphite.
The use of porous carbon is suggested by Dietz et al. (U.S. Pat. No. 2,760,598) for storage of liquified gases, including liquid air, hydrogen or nitrogen. Savage (U.S. Pat. No. 2,626,930) has proposed using chemically active graphitic carbon for adsorption of gases.
Modification of carbon with metallic salts has been disclosed by Keyes (U.S. Pat. No. 1,705,482) to produce a material appropriate for the storage of gas or liquid materials.
Hecht, in U.S. Pat. No. 3,387,767, has recited a cryosorption pumping element for a high vacuum pump, comprising a mass of sintered fibers and sorbent powders.
Other methods proposed for the storage or transportation of hydrogen include the use of metal hydrides and chemial hydrogenation/dehydrogenation. Metal hydride systems have been investigated extensively, for example, storage of hydrogen as iron titanium hydride FeTiH.sub.1.95, see, Reilly, "Applications of Metal Hydrides," in Andresen et al., ed., "Hydrides for Energy Storage," New York, Pergamon Press (1978).
Presently available cryopump adsorption elements have limited capacity for hydrogen, because attempts to increase the capacity of the cryoadsorption elements by using adsorbents of large particle size have been unsuccessful. The unacceptability of cryoadsorption elements made from large granules of adsorbent has been attributed to decreased thermal conductivity and decreased diffusion, inherent in large adsorbent granules. Prior art cryoadsorption elements therefore have been constructed from irregularly-shaped carbon particles having an average diameter of about 1 mm for maintainance of acceptable diffusion and thermal conductivity properties. See, Hands, "Recent Developments in Cryopumping," Vacuum, vol. 32, pages 603-612 (1982) and Visser et al., "A Versatile Cryopump for Industrial Vacuum Systems," Vacuum, vol. 27, pages 175-180 (1977).
Hydrogen can also be stored in heavy metal cylinders, so as to avoid the cost of liquefaction. However, use of cylinders is not particularly attractive economically.
There is, accordingly, a need for improved methods of adsorbing and storing hydrogen, particularly at cryogenic temperatures.
It is an object of this invention to provide an improved method, using carbon, having a high nitrogen BET apparent surface area, for rapidly adsorbing and storing hydrogen in the context of cryogenic pumping.